1. Field of the Invention
The invention relates to a hydrocarbon synthesis process with increased catalyst life. More particularly, the invention relates to a slurry catalytic hydrocarbon synthesis process employing a supported cobalt metal catalyst in which catalyst half life is increased by using a syngas feed containing less than fifty parts per billion of nitrogenous, catalyst deactivating species.
2. Background of the Invention
Slurry hydrocarbon synthesis (HCS) processes are known. In a slurry HCS process a synthesis gas (syngas) comprising a mixture of H.sub.2 and CO is bubbled up as a third phase through a slurry in a reactor in which the slurry liquid comprises hydrocarbon products of the synthesis reaction and the dispersed, suspended solids comprise a suitable Fischer-Tropsch type hydrocarbon synthesis catalyst. Reactors which contain such a three phase slurry are sometimes referred to as "bubble columns", as is disclosed in U.S. Pat. No. 5,348,982. Irrespective of whether the slurry reactor is operated as a dispersed or slumped bed, the mixing conditions in the slurry will typically be somewhere between the two theoretical conditions of plug flow and back mixed. It is also known that Fischer-Tropsch type catalysts useful for forming hydrocarbons from a syngas are rapidly, but reversibly deactivated by certain nitrogenous species in the syngas feed, particularly HCN and NH.sub.3. Syngas made from hydrocarbon feedstocks which contain nitrogen (i.e., natural gas) or nitrogen containing compounds (i.e., resids, coal, shale, coke, tar sands, etc.) invariably contains HCN and NH.sub.3 which contaminate the reactive slurry and deactivate the catalyst. Certain oxygenates and carbonaceous compounds which are formed in the slurry as by-products of the HCS reaction are also believed to cause rapid deactivation. Deactivation of such catalysts by HCN and NH.sub.3 may be reversed and catalytic activity restored (rejuvenated) by contacting the deactivated catalyst with hydrogen or a hydrogen containing gas (rejuvenating gas). Deactivation of such catalysts by these species is reversible and catalytic activity is restored (the catalyst rejuvenated) by contacting the deactivated catalyst with hydrogen either continuously or intermittently as is disclosed, for example, in U.S. Pat. Nos. 5,260,239; 5,268,344 and 5,283,216. While methods have been suggested for reducing the HCN and NH.sub.3 content of syngas down to about 0.1 ppm (100 ppb) by catalytic hydrolysis (U.S. Pat. No. 4,769,224) and chemical scrubbing (U.S. Pat. No. 5,068,254), it has now been found that even as little as 100 vppb of a combined total of HCN and NH.sub.3 in the syngas will result in a catalyst half life of only four days for the case of a supported Co metal catalyst in an HCS slurry. It has now been found that reducing the level of the HCN and NH.sub.3 catalyst poisons in the syngas below 50 ppb produces increased catalyst life and requires less catalyst rejuvenation. A method for achieving such low levels has also been found and is disclosed in U.S. Pat. No. 6,107,353.